NEW SERUM GROUP, GM(P).

The agglutination that occurs when rheumatoid arthritis serum Pond is added to erythrocytes sensitized with anti-D serum Moore is inhibited in the presence of some normal serums. The inhibitor, tentatively named Gm(p), is associated only with 7S gamma globulins and is apparently different from other previously defined serum groups. It is much more common in Caucasians than in Negroes, and probably is determined by a simple dominant gene.